Seems like the DSL for expose and format_with is not working when passing blocks unless you use explicit parenthesis.

To debug this in isolation, I've use the following code snippet:

 class Comment include Grape::Entity::DSL attr_accessor :text entity :text end class Post include Grape::Entity::DSL attr_accessor :title, :content, :comments entity :title, :content do format_with :array_counter { |array| array.size } expose :comment_count { |message, options| message.comments.size } expose :comments, :format_with => :array_counter end end

Trying to present a "Post" entity with two "Comments" then throws:

syntax error, unexpected '{', expecting keyword_end 

The error is thrown while interpreting the format_with or expose lines (in this case format_with since it comes first)

If I change the format_with and expose declarations to include explicit parenthesis like this:

 format_with (:array_counter) { |array| array.size } expose (:comment_count) { |message, options| message.comments.size }

I then get the expected JSON output

{"title":"Post title","content":"Post contents","comment_count":2,"comments":2} 

Tried it also with explicit creation of the entities subclassing Grape::Entity instead of including Grape::Entity::DSL, same result

Running ruby version: ruby 1.9.2p320 (2012-04-20 revision 35421) [x86_64-darwin11.4.2] under Mac OS X 10.7.5